Circling behavior is often observed in animals, but it is less well known that this behavior can occur in humans as well. It is often much more subtle in humans. For instance, a human may not necessarily walk monotonously in circles, but he might have a tendency, for example, to turn more to the left or more to the right during the course of otherwise normal movements.
Some research has indicated that this turning behavior can be related to the relative dominance of one half of the brain (cerebral hemisphere) over the other. It may also be related to abnormalities of the brain, and thus a knowledge of the tendency of neurological, or psychiatric patent to turn more frequently in one direction may be helpful in diagnosing that patient. This turning information, when objectively quantified, may also be useful for measuring the effectiveness of certain types of medication.
Circling behavior is for the most part dopaminergically mediated and related to asymmetry in dopaminergic activity between the left and right basal ganglia or left and right frontal cortex. As a rule, animals rotate toward the hemisphere with lower striatal dopaminergic activity. (Bracha, H. S., Life Sciences, Vol. 40 pp. 1127-1130) It may give an indication correlated with schizophrenia in human subjects, since schizophrenia is also related to dopaminergic activity. Other reports indicate that turning behavior may also be affected in Parkinsonian patients.
Thus it is desirable to accurately measure the turning tendencies of humans, both for research and potential treatment. It is desirable to be able to record the total number of left turns and of right turns that the patient has made over some time period, say for four or eight hours. In addition, it is desirable to record the total number of left and right half and quarter turns made during the same time period. This latter information is useful, since people make many more of these turns than they make complete 360.degree. turns. If the recorded numbers are larger, the statistical accuracy of the measurement is increased.
An early device (S. D. Glick) was built using a standard hand-held compass consisting of a "needle" pivoted above a card. The position of the needle was sensed by photoelectric cells, and appropriate electronics computed the number of turns in each direction and stored these cumulative totals for later readout by a researcher or physician. This prior device suffered from the following disadvantages: The photoelectric cells required a relatively large electrical power, which limited the measurement time on a given size of battery. The large diameter of the compass made the instrument relatively bulky. The nature of the pivots on such compasses is such that they are relatively sensitive to shocks and thus relatively unreliable. The pivot arrangement of such compasses is also such that they will jam and not turn if the compass is tilted significantly from the normal horizontal position. Since these instruments must be worn on the belt of a patient, they are tilted back and forth most of the time that the patient is walking around, precisely when they should be making an accurate measurement. Power drain was higher, size was larger, and this device was difficult to construct.
Some marine and aircraft compasses could overcome this tilting problem by mounting the compass in a set of gimbals. Such an approach is not practical in this field, because it unduly increases the bulk of the instrument.